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EPE Journal Volume 01-3 - Papers
- The application of double-fed motors for traction drives
- Impact of Turn-off Semiconductor Devices on Power Electronics
- Off-Line Optimized Synchronous Pulsewidth Modulation with On-Line Control during Transients
- Phase-Current Control and Current-Component Control of Asynchronous Machines fed by Low Pulse Frequency Inverters
EPE Journal Volume 01-3 - Editorial
By P. D. Evans
The Editorial of the EPE Journal Volume 1 N°3, "The Future of Power Electronics", written by Prof. P. D. Evans, Member of EPE Association's International Steering Committee.
EPE Journal Volume 01-3 - Papers
By G. M. Brown; B. Szabados; R. Belmans
For very high power applications, supplying three phase variable frequency power to the rotor windings of an ac machine results in a double-fed configuration that allows for example for slip power recovery and speed control over a limited speed range. This paper explores the additional performance gains that are possible when both the stator and the rotor are connected to independently controlled three-phase power sources. In particular, the use of two independently controlled cycloconverters to feed such a double-fed motor (DFM) takes full advantage of the cycloconverters very high power and smooth torque capability at low speeds and doubles the upper speed limit available compared to a standard cycloconverter system. This configuration also allows the frequencies of both stator and rotor power to be chosen independently of the rotor speed, with the result that both converters can continually operate in such a way as to minimize harmonic generation, avoid saturation problems at low speed and to control the power factor at the motor terminals.
The paper presents the results with help of the circle diagram for the DFM, which is very usefull for visualizing the complex interaction between voltages, currents, frequencies, speed and torque production.
By K. Heumann
Turn-off semiconductor devices have vastly promoted modern power electronics during the last decade. Included are bipolar power transistors, Field Efficient Transistors (MOSFETs) Gate Turn-off Thyristors (GTOs) and Insulated Gate Bipolar Transistors (IGBTs). Additional Elements are Static Induction Transistors and Thyristors (SITs and SIThs) as well as MOS Controlled Thyristors (MCTs) for higher frequency applications.
The present status of semiconductor power devices is discussed including switching behavior, losses, gate driver, snubber, overcurrent and protection. The standard control is nowadays pulse width modulation. Resonant circuits are growing in importance because they allow for higher frequency, lower storage components and transformers and reduction of switching losses in semiconductor devices. Main field of application are discussed and future trends given.
By J. Holtz; B. Beyer
High power pulse-width modulated (PWM) inverters are generally operated at low switching frequency in order to avoid excessive switching losses. This produces increased current waveform distortions, additional machine losses and torque harmonics. It is therefore expedient to adopt optimal PWM strategies for their control.
The technique of optimizing the pulse sequences by off-line calculations is advantageous as far as the steady-state performance is concerned; however, the modulator is nonoptimal and unpredictible during transient operation. Any change of the steady-state leands to transient overcurrents. This drawback is eliminated by the implementation of a control algorithm for the harmonic currents. A trajectory controller ensures that the current vector is guided along precalculated optimal trajectories, maintaining optimal current waveforms also under transient operating conditions.
By E. Seefried; J. Kaschel
This paper discusses some problems of current control of asynchronous machines fed by thyristor inverters. The possibilities of the phase-current and current-component controls are pointed out and are compared, where the design of the so-called decoupling network II has an important influence on the response of the current feedback control. Some hints for the controller adjustement are given.